Electron-discharge device



3 Sheets-$heet -B. F. MIESSNER ELECTRON DISCHARGE DEVICE Filed May 15, 1927 June 18 1929.

wweutoz Bagel mill EMz'eJSIler June 18, 1929. E NE 1.718.059

,- ELECTRON DISCHARGE DEVICE Filed May 13, 1927 3 Sheets-Shet V 2 &

. h A: w *1 P-q I a I e x -wwentoz Bery'amin FMZJ YZzer June 18, 1929. B.- F. MIESSNER I ELECTRON DISCHARGE DEVICE Filed May 13, 1927 3 Sheets-Sheet 5 anoeutoz Begi'arkin lFM' iiffize r Pat nted June 18, 1929.

JSTATE minimum 1'. irmssunn. or soon: oaaueninnw JERSEY.

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Applicatlon fll ed lay 13, 1927. I Serial No. 191,195.

This invention relates to electron discharge. vacuum tubes and like devices, and to an electric' signal receiving system employing one or more of such tubes as rectifiers, ,re-

peaters or amplifiers; more particularly to such a system wherein sources of unsteady potential areused for energizing one or more of the vacuum tube circuits.

' Whensources of ordinary unsteady potential are used for energizing vacuum tubes in circuits there is a tendency to produce low frequency disturbing current variations or bum in the plate circuits of thetubes which materially interferes with the operation of the system. Such variations may arise from a number fof causes. 1

Thus, when the plate or output circuit is energized from a direct current commutating machine, or from an ordinary alternating current rectifier and filter which filter does not effect a complete smoothing out of the rectified current, the current in the plate circuit is subject to periodic variations or ripples.

Also-when the tube filament is heated by ordinary alternating, such as cycle commercial current, or other unsteady current a numt ber of effectsare produced, which may contribute to a greater or less extent to the production of disturbing plate current variations. Thus during momentary recurring periods of low current, the temperature of the filamentfalls and the electron emission from the heated'filament is momentarily reduced which tends to decreasethe flow of electrons to the plate electrode.

Also when unsteady current is used for heating the filament, the variations in the difference of potential between different portions of the filament tend to cause variations in the plate current. It appears that portions of the filament which are momentarily of higher positive potentials than other portions have the effect of diverting from the plate some of the electrons emitted from the lower potential portions of the filament, thus periodically robbing the .plate of .some of its supply of electrons. This robbing effect increases with increase in potential difference between the different portions of the filament, and I-also find that the robbing effect is greater when thehigh. and low potential portions of the filament are spacedcloser to one another than'when they are spaced farther apart. a

. In vacuuni tubes employing grids, the grid I is generally connected "to some point of the filament supply circuit so as to maintain the grid at a fixed normal potential" relative tori some point of the filament. Thus when-the grid is connected to a mid" potential point of the filament supply circuit, the normal potential of the grid is that of the mid oint of the filament. If, when so connecte ,the filament is heated by alternating current all points of the filament except the mid-point -.will vary periodicallyin potential withrespect to the grid. When the current is flowin in one direction through the filament the grid will be positive with respect to one-half of the filament and negative with res ect to the other half, and when current is owing in the opposite direction the grid will be 'negatiye with respect to the one-half and positive withrespect to the other. The grid,

which is-thus always positive with respect to half of the filament, affects electron emis- ,sion from this half of the filament and tends to cause variation in the plate current in a manner'quite similar to theefi'ect which the higher potential portions of the filament have on the lower potential portions of" the filament, and which I have referred to above as the robbing effect. This grid effect, simi larly to the robbing effect, increases with increase in potential difference between the grid-and the portions of, the filament which n are at'lower potential. I

I also find that among the factors or con-.

ditions' which affect the degree of production of distributing variations in the plate current arethe plate voltage and the grid: biasing voltage. Generally the greater. the plate voltage the less effective is the tendency to produce such variations. When a negative grid biasing voltage is employed, I find that an increase inthe negative-grid bias within limits tends to increase the hum effects; an increase in the negative grid bias being-similar in its effect to the effect caused bydecreasingthe plate voltage 1 When the plate circuit of one tube is coupledto the grid-circuit of the succeeding tube,

tubes is designed for radio frequency, as in the-case of a multi-stage radio frequency amplifier. lt appears. that the unsteady-energizing currents in the radio fre uency tube circuits have the effect of causin t ie high frequency signal currents received y the tube to' be modulated. at low frequency, and these modulated currents are readily'passed ()lirtO the succeeding tubes by the high frequency couplings to be subsequently detected in t e deteeter stage to become an audio fre uency.

. In my eopending application, erial No. 117,07 6, filed June 19, 1926 I described the effect which certain of the above mentioned conditions have in the production of hum. I

pointed out that the effect caused by variations in filament voltage, which I term the robbing effect, and the effect-caused by varia' tions of'temperature ofthe filament, which 1 term temperature effect, occur at a frequency double that of the frequency of the current in the filament, and these two effects oppose one another in phase relation in such a Way that the-net effect in the plate circuit due to the combined action of temperature effect and robbing effect-may be much less in amount than either the temperature effect or the robbing effect alone. In said application I dis-.

close a multi-sta e signal receiving system and, a s a means or reducing disturbin variations in the plate circuits, I disclose a t treeelectr'ode vacuumtube of special construction Zyhieh I employ in certain stages of amplificaion.

In the present invention, which has for its object thereduetion of hum, I also make useof a special vacuum tube which is of novel and nnproved construction, particularly with respect to the form and dimensions of its filament.- .In the preferred embodiment of my improvedtube for the common use of received radio s1gnal amplifying and repeating, and like purposes, t efilament' is'straight and short preferably from .75 to 1.25 inches in lengt It is approximately circular in cross section with-a relatively-large diameterof from approximatel 4.5 to 9 mils orxmore, and' ithas sufficient sur ace to supply enough elece" as a fcient electrical energy can be supplied to the filament to heat it to its operating temperature at a voltage considerably less than two volts.

The tube having a filament of the chair- I the acteristics above 1 described is particularly adapted for use with alternating or'other unsteady current in the filament. Due 'to the large diameter the filament has high heat .inertia or heat storage capacity and as a result the temperature of the filament falls little during recurring periods of low cur i ves greatly increased electron emitting sur ace andper- I rent? The increased diameter mits the tube to be operated-at a very low temperature at thesame time providing suf-- ficient electron emission for operation.

Operating the filament low current when there is not sufficient elec-, trieal energy'supplied the filament to mainv at. low temperature is a distinct advantage. During periodsv of tain its temperature the filament momentarily cools.

ture during the periods of low current is As it cools its rate of electron emission decreases. The drop in te dependent on the rate uponwhich the filament is losing heat by radiation. As; this rate is approximately proportional-to the fourth power of the'temperature the fin,

ment, when operated at low temperature, $3

will lose much less heat and will drop less in temperature than the'filament operated at high temperature. In point of fact, with my low temperature filament, the actual drop'in temperature during periods of low.

current is, so small that the decrease in'th rate of emission is. actually less than thedecreaselin the rate of emission of a filamen operated at high temperature, and this is true in spite of the fact that in order to p'rovidesufiicient electron emission at lovy' tern; per'ature my filament must have a much? greater rad'ating surface than a filament as;

signed for operationat high temperature. The application of the necessary energy} to produce th'er'equired electron emiss1'on aft-1" low voltage results in minimizing thega ob effect because no portion of the filament,

.wilfat any time be of much higher otential than any other portion, and the big er posiotentialportions of the filament- .not f ivert from their normal path to. the

plate to any considerable extent,electrons; ortions. 1'16 emitted from the flower. potential Furthermore as the filament which employ.

in) t.

.is straight, high and lowpo'te'ntial portions- .of the filaments are locateda maximumj dis; tance a art,-which alsominimizes'the-rob bing e ect.;

1 also find s ml at. tolreduce still,

effect by a proper selecfurther the robbin 5 grid biasing voltages.

tion of 1 late an tial portionso the. filament have less effect towards diverting electrons awayfrom-the 'With'a highergilate voltage the high potenplate. A negative grid bias has an effect similar to areduction in platev'oltage; That is, .it increases the tendency of the'liigh po-.

- tential portions of the filament to divert electrons from the plate. With a relatively ion izb

low plate voltage therefore I use a relatively low negative grid bias and with higher plate voltage a higher negative grid bias. In practice I employ with a tube such as described plate voltages of the order of 100 to 150 volts and grid biasing'voltages of from -3 t 5 volts when the tube is bein operated as a radio frequency or an. au freways portions of the filament which vary quency amplifier. As previously explained, with the grid connected to a point of the alternating current filament supply circuit, there are alperiodically inpotential with respect to the grid, and the normal efiect of such variations in potential is to produce disturbing variations of the plate current. This tendency,

as also previously explained,-increases with incieased amplitude of potential variations between such portions of the filament and the grid. It will be apparent thatheating the filament by alternating current of comparatively low voltage minimizes the disturbing variations arising from this source.

From the above discussion it will be seen that in my improved tube the temperature eifect and the robbing efiect are each reduced to a minimum. As these effects, as previously stated, oppose one another in phase relation,

'- nomical to manufacture.

it will be apparent that in operating my im- 1proved tube with unsteady current in the lament the actual hum produced in the plate circuit by'the conjoint action of the temperature androbbing effects will be very small." 'In operation of this tube not only have I reduced both the temperature and robbing effects, but their values over the range of filament, grid and plate: otentials at which the tube operates efiicient y as a re eater are so small and so nearly equalthat. t e resulting hum in the plate circuit due to the unsteady filament heating current is practically negligible. a v

The use of a straight filament of short length simplifies the mountinglofthe filament in the tube and makes the tube more eco- As the filament is of large diameter it is strong, durable and has a relatively .long life.

Receiving. systems employing tubes with relatively thin or long filaments are particularlysusceptible to the production of disturbing m'icrophon'ic effects. The thin or long filaments are easily set in vibration when the tube is arred or when sound vlbrations ..reach the tube from the loudspeaker, and

such vibration of the filament produces disturbing variations in the plate current which are reproduced as soundin the loud speaker or telephones. To avoid this disturbing effeet, it has been the practice to mount tubes on spring sockets which act as shock absorbers to prevent jars or other vibrations reaching the tube. The filament of the tubeconstructed in accordance with the present invention,

radio and audio stages of amplification, and a detector stage, and I preferably employ my improved tube in each stage of this system.

The filaments of all of these tubes areheated by alternating current and the plate circuits are energized from a source of alternating current through a rectifier and filter. .In ad-v dition to utilizing my improved tube, the sys-;

tem embodies additional means for eliminating any hum in the plate circuit of the last tube, which may result from. fluctuating potentials supplied to the plate circuit bythe.

filter, or any residual hum arising from the use of alternating current in the filaments.

Other advantages of my invention will appear from the following description taken in connection with the accompanying drawing,

electrode vacuum tube showing. one embodiment of m invention. Fig. 2 is an opposite side elevation of the same tube with a portion of the tube platetaken away to show the grid and filament. 'Fig. 3 is a top plan view of the I tube. Fig. 4 is a'curve diagram illustrating .the results'of an operatin "shown in Figs. 1 to 3, the tub ating as an audio frequency amplifier. Fig. 5 is acurve diagram explanatory of the retest on the tube e under test opersults obtained in the operating test of Figure 4; Figure 6 is a diagram showing the result wherein Fig. 1 is a side elevation of a threeof another test on the same tube, the tube being operated as a detector during this test, Figure 7 is a diagram of a multista receiving systememploying my improved tubein each stage, and Fig. 8 is a view similar to Fig.2 but showing a tube having two filaments connected inthe supply circuit in parallel with one another.

Figs. 1 to .3 show one form of my improved tube particularly suitable for the power re-v signal quired'in the amplification and repeating of radio reception with a loud speaker, in substantially its exact size and dimensions. This tube comprises a filament 10, grid 11 and plate 12. The filament 10 is straight, approximately 1 4 inches long, nine mils in diameter and is formed of platinum-nickel wire, coated with oxide of strontium and barium. When an alternating current of .9 effective Volts. is applied to the terminals of the filament, the current through the filament is approximately 1.25 effective ampcres, which is a normal filament current for proper operationof the tube. This current heats the filament to a .50 ff curvesv the results of a comparative hum test made on twov tubes, one of which is a black red heat, that is, a dullred heat which is but imperfectly visible,

7 The filament connected at its ends to leading-in wires, 15 and 16, which are sealed 7 through the glassneck of the tube, the wires 1-5 and '16 serving to support the filament in f the position shown, The grid 11, which sur-j j rounds the filament, isa fiat coil of fine wire wound on spacedvertical rods 18, the lower ends of which are attached to supporting wires 19 sealed in theglass neckof the tube,

one of the wires 19 extending neck and formingthe leading-1n terminal of through the the grid. 1

one of'the wires 23 extendin The plate 12, which is spaced from and surroundsthe grid 11, is formed of two thin sheet metal side members 20 and 21, bent toward one another .and joined together near their side.

edges. The outer edges of the members 20.

and 21 are pinched around supporting rods 22 which are secured at their lower ends to wires 23, sealed in the glass neckof-the tube, I through the neckand forming the leading-1n terminal of the plate.

1 Thetube shown in Figs. 1 to 3 has a single straight filament. In other tubes construct- 'ed by me, I have employed two or a plurality of spaced filaments mounted parallel .to one another in the central plane between and parallel to the side members 20 and 21 of the plate 12. These filements have substantially the same form, dimensions and composition as the filament 10 of-the tube shown in Figs. 1 to 3. The filaments in the modified tube are connected to the supply circuit in parallel v with one another and are operated'at approximately the same or a somewhat less voltage .than the filament of the tube shown in Figs.

1 to 3. In Fig. 8 I have shown a tube of this character wherein two filaments 10 and 10" areeach connected at their opposite ends to the respectiveleading-in wires 15 and 16, thus-connecting two filaments in parallel in the supply circuit. It is readily seen that with such a two-filament tube, the electron emisslon ditrib tion with respect to the surrounding grid "im 'roved.

nd plate structures is greatly n Fig. 411 show diagrammatically by tube hereinbefore described. This test shows I the, amount of hum produced in the plate circuit of the herein described tube when'its filament isheated by a cycle alternating "cur-' rent, and the plateand'grid biasing'voltages V are respectively 130 and 4 volts, these being the plate and grid biasing voltages suitable for efficient operation of the tube as an audio frequency amplifier. 'In the Figure 4: diagram; the lower row of abscissaewalues represent the effective alternating current voltages applied to the terminals of the filament of t 0 tube herein described, which I term the tn 1 T. Ordinates represent the hum in volts, and the curve E represents the hum-produced 1n the plate circuitfor values of filament voltages ranging from .44 volts to .95 volts, within which range of voltage the tube T operates efiiciently as an amplifier.

ferred to, I describe the results ot a similar hum test made on the s ecial' tube described and shown in that apphcation, and 1n Fig. 7

I In my copending application above reof the drawing of that application I illustrate by means of a hum'curve results of the test on such tube over a range of filament voltages of 2.6 to 6. The tube in this test was operated at a plate voltage of 135 and a grid biasing volttags of 4.5 volts these being values at which the tube operates effectively as an audio frequency amplifier.

tube described in my copending application,

, To furnish a comparison I, between the amount of hum produced by the which I will term the tube T, and the tube T of the present application I have repro-' duced' in Fig. 4 of the accompanying drawing as curves E',, and L. on a greatly enlarged scale the hum curve E and th plate current curve I respectively, shown n Figure 7 of my copendingapplication. The upper row of circuit of the present tube is considerably less than the hum produced by the former tube throughout practically an entire range of fila ment voltage variation equal to.50% of the maximum. Both curves'reach a maximum early in increasing the filament voltage, the maximum of curve E being considerably less than half the maximum of curve E As the filament voltages are still ;further in creased, the hum ofeach' tube is reduced until it reaches a minimum .ior each tube at approximately .725 filament volts for tube '1 current curve for the tube"! of the present ap- E and I and 4.8 volts'for tube T; the hum volts at these minima being substantially the same.

Further increase in filament voltage increases I the hub of bothtubes, but in the case of tube the hum increases at a much-greater rate T! than does [the humof tube T. Thus over racticallvthe entire ranges of filament voltages within which ranges these tubes operate most efliciently as amplifiers, the hum volt- .age of" tube T is considerably less than the I hum voltageof tube T.

This advantage is gained through the particular construction of the present tube, par,

ticularly b the use in such tube of the special filament a va described. In operating the tube T in the manner above set forth,'not only is the temperature effect and the robbing effect each reduced to a minimum, but as these two effects tend to oppose one another in phase relation, the actual hum produced in the plate circuit'by the combined'action of both effects is practically negligible throughout a Wide range of filament voltage variation.-

In Fig. '5, I illustrate how the hum effectrepresented by the hum voltage lcurve E, of Fig. 5 may result from the combined action of the temperature effect and-the robbing effoot. The temperatureeifect is-represented by the curve E, of Fig. 5 and it will be seen that this effect reaches a maximum approximately where the filament voltage plate current characteristiocurve is steepest, that is,

when a small change in the voltage of, or current in, the filament, and therefore small change inlfilameut temperature, makes the greatest change in effective space or plate current. Beyond this point, the temperature effect decreases, becoming less as the plate current curve flattens out, which shows that v even though the temperature of the filament is much higher in this region than at the -couditions at a point of lower temperature -to be usefully neutralized by the voltage-efsteepest portion of the curve the effective change of space current with change of tem-' peratui'e atthis flatter part of the curve is much smaller. Thus, while it is quite 11nportant to use a filament having an emissive coating, such as barium and'strontium oxides,

which permits of useful degrees of emission at low tenuperature, and to otherwlse decrease the overall tendency-to avoidvaryingq-the emission by temperature effects,-.s.as by the use of large mass of the filament, yet the com-' .paratively large amount of h'umas shown by the curves at points of lower temperature 'of filament clearly brings out that the mere resort to low temperature and large" mass does not exhaust all the possibilities in the right direction. Further analyzing,'.Fig. 5,

which shows the characteristics of a tube designed to operate with very low temperature and large mass of filament conditions, comparatively speaking from the point of view of common tube practice, makes it clear that the hum voltage E, due to temperatureefiects is large, and too large even under the special feet; but by going to a'higher temperature, where space current approaches saturation to temperature increase, the temperature effect hum becomes very small and is nicely overcome by a small voltage effect.

to the filament, because with increase po-' tential difference between. different portions ofthe filament there is a greater force-act- Ev represents the robbing effect curve'and shows the h um effect due to increasing alternating potential difference across the fila- ,ment terminals'. The'robbing effect increases with ,increasingalternating voltage ap lied robbing eflects in the present tube T are much less than the corresponding eifects in tube T.

As I explained in my copending application above referred to, the temperature effect and robbing effect are opposed to one another in phase relation. If these two effects were displaced in phase by exactly 180 and the wave form of both effects were the same, the combined action of both effects would berepresented by. the curve E in Figure 5, whose ordinates are the difierences between the ordinates of curves E, and E,,. Where curves E, and E, intersect, that is, where the ordi-. nates are equal, theresulting hum would be zero. As pointed out in said application due to the heat inertia of the filamentthe changes in temperature of the filament do not exactly coincide with changes in filament current, and as a result the temperature effect and robbing effect may not be displaced from one another exactly 180 and therefore not completely neutralize one another. Furthermore,

it is probable that the wave form of the temperature effect is not exactl the same as the wave form of the robbing e ect. Due to such differences in wave form and the displacement of the two eflects by an amount different often desirable to make the opposing effects small. I

I have also made similar tests on the tubes T and T as radio frequency amplifiers, The results obtained are similar to those ind cated in Fig. 4 and'show very much less hum for the tube T than for tube T.

For the purpose of brevity and definiteness in setting forth the invention to be defined in the claims annexed hereto I give the following distinctive terms and definitions thereof as applied to the characteristic curves of my improved tube which are shown in Figs. 4 and 5 and hereinbefore fully described.

Emission durve.-The curve-I1 in Fig. 4, which graphically showsthe relation of the space current between filament. and plate to the filament potential as the filament poten- 'tial is altered to alter. the temperature ofor emission from the filament while the filament is under the influence of energizin potentials applied to the plate and gm for operation of the tube as an amplifier butiirrespective ofthe signal variations impressed uplon such potentials during operation of the "tu )e.

of maximum curvature at the upper bend of the emission curve, and beyond whichrela-.

:ti velylarge change in filament temperature tive space current. V

or voltage produces but small change in efl'ec- Origin of emission saturatiQn.'-Thepoint H um cmwe.-The curves E, and E' in Fig.

the radio and audio stages of the system.

relation between amplitude of space current variations resulting from filament current and voltage variations and the average filament voltage as the filament voltage is al tered when the filament is supplied with alternating current in the presence of plate and grid electrodes energized for normal operation of thetube as an amplifier but irrespective of the si nal variations impressed upon such potentia s during operation of the tube, which curve depends upon the combination of the varying temperature and varying electrical efl'ects arising from the alternating current energization.

Hum mim'nmwm-The region in the bum curve where the neutralization as between the varying temperature efiects and the varying electrical eflects is maximum, which region is typified in Fig. 4;, as that portion of the curve E included between the filament.

potentials 0.6 and 0.8 volts and that portion of the curve E' included between the filament potentials 4.5 and 5.0. a i

It has heretofore not been'practical to heat the filament of a detector tube with alternating current, because of the excessive humproduced in the plate circuit. In my copending application, I illustrate a multistage signal receiving system wherein the tube described in such application is used in n the radio. and audio frequency stages the tube filament is heated by alternating current. In the detector stage, to avoid the excessive hum that would be produced if the detector filament were heated by alternating current, I provide means for heating the detector tube filament by direct current. The tube described in the present application may be used as a detector as well as an audioand radio frequency amplifier, and when used as a detector, its filament may be heated by alternating current without the production of any appreciable hum.

In Fig. 6 I show b the curve E, the hum in the plate circuit of t 1e tube T when this tube is bein used as a detector with its filament heatedliy 60 cycle alternating current, and I show by the curve E h the corres onding hum produced in the plate circuit 0 the tube T of my copending application. Ordinates for each curve represent hum Volts. The 'lower row of abscissae values represent the effective volts across the filament terminals of tube T ranging from .6325 volts to .8625volts and the upper row represent therefi'ective volts.

across the filament of tube T ranging from 2.6 volts to 3.4 volts; these being ranges of voltage within which therespective tubes operate efiici'ently as detectors. 'The plate voltage of tube '1 in this test was 30 volts and its grid bias +3.0 volts, the plate voltage of tube T was 27 volts and its grid bias 4.5

that is as rectifiers with incidental amplification of signal current, was about the same. When the same signal current was impressed on the. grids of the two tubes, this current being such as toproduce a fairly loud sound in a loud speaker associated with the plate circuits of the tubes through two stages of. audio amplification, the signal volts represented by thecurves E and E' were produced in the plate circuits of the respectivetubes T and T. c

It will be seen that the bum produced in the plate circuit of the tube T is enormously greater than the-hum in the plate circuit of tube T, and the hum oftube T- isso great in proportion to the signal volts that it completely masks the signal received. On the other hand, the humin the plate circuit of tube'T is so small in proportion-to the si nal volts that its effect on the signal received is practically negligible.

An'inspection of the curves E andE'g of v Fig. 6 shows that the bum for both tubes increases steadily wlth increase in potential across the filament terminals and in this respect both curves are similar to the curve E of Fig. 5, which represents the robbing efi'ect of the tube T vvhen used as an amplifier. It will also be noted that the humps or maxima which occur at the left of curves E, and E' in Fig. 4 have completely disappeared in the curves E, and E,, of Fig. 6. 'lhesehumps, as shown by the curve E in Fig. 5, are caused'by the temperature effect. The similarity of the curves E, and E h of Fig. 6 to the robbing effeet curve E,, of Fig. 5, as well as the absence of the humps, indicate that in operating the tubes under the plate and grid biasing voltages which render the tubes suitable for use as detectors, the temperature effect is practically zero and the hum produced is almost entirely due to the robbing eflect. The extremely small hum in the late circuit of tube T seems therefore to be ciiie toa large extent to the low voltage at which the tubeT is operated, and to its straight form of filament.

If some one portion of a vacuum tube .filament were spaced considerably nearer to the plate or grid of the tube than other portions thermore, the filaments in these tubes are ofsuch form. and so located with respect tothc grids and plates that the alternating mag- 4 netic flux produced in the neighborhood of the 1. 30

filament, caused by the alternating filament lll) ' tions in the flow of electrons rom the filament to theplate, an effect in phase alliance with the voltage or robbing eifect.

In Fig. 7 I have shown one system in which my improved tube may be employed. In this system the filaments of all the tubes areheated by alternating current and the plate circuits are supplied with current derived from'alternating current source through I low voltage to the filaments oftubes 50 to 53 a rectifier and a filter. y l Tubes 50 and 51 in Fig. 7 are radio frequency amplifying tubes; tube 52 is a detector p and tubes 53 and 54 audio frequency amplifying tubes. At 60 is shown an antenna for collecting radio signaling energy having the primary 61 of the transformer 62 in series therewith, the antenna being grounded at 6-3. The-secondary winding 64 of the transformer 62, cooperating with a variable condenser 66, permits tuning of the grid circuit of vacuum tube- 50 to the frequency of-any desired incoming signals. The second vacuum tube 51 is selectively associated with the first vacuum 1 tube-50 through a transformer 68 and variable condenser 69. The detector tube 52 is selectively associated with the second radio frequency tube through a transformer '70 and Variable condenser- 71. The first audio fre-' quency tube 53 is associated with a suitable audio frequency transformer 7 4 shown to have a resistance 7 6 connected across its secondary winding, the grid circuit oftube 53 being adjustable to connect with different points of the resistance 76 so as to control the volume of sound signals produced. The second audio frequency amplifier tube 54 is associated with the first audio frequency amplifier tube by action of the ehoke coil the system for'amplificat-ion and detection through a suitable audio frequency transformer 78. A loud speaker or other suitable signal translating device 80 is energized by the highly amplified signal currents from the final amplifier 54. The loud speaker is connected between the filament and plate of the tube 54 through the capacity coupling condenser 82, the signal currents, being diverted to the loud speaker through the condenser 82 I 83 in the plate circuit of tube 54. v I I The two radio frequency stages are shown to be neutralized against oscillation production or' excessive regenerative amplification caused by plate circuit reaction on the grid through the internal capacity of the tube. by

condense-rs 84 and 85 connected to the grids of theirrespectivetubes from a tap connection .to the secondary windings-of the transformers in the plate circuits of these tubes,

For the -purpose of supplying-energy to of'the signals received I show at a-transformer, the primary 91 ofwhieh is'adapted to be supplied with alternating current from the usual house lighting system. Connection between the primar and the supply system ma be made by a exible cord connector, 94 an a plug 95 adapted for insertion in the ordinary house lighting socket. switches 96 and 97 and fuses 98 may be included in the connection to the primary and, if desired, an adjustable tap 99 maybeprovided for including a greater or lesser number of turns of the primary in circuit with the supply *mains. A secondary 100 of the transformer 90 supplies heating current at Suitable of the'transformer 90. For the power tube 541 may employ a tube of the same general a type as that shown in Figs. 1 to 3, except that its filament is somewhat longer than :the filament of the tube shown in these figures and its filament is heated by current/at 'a somewhat higher voltage. As any hunrgenerated in tube 54 is not further amplified I may, if desired, employ for this tube any of a munber of power tubes now available.

Connected across the secondary 101 is a potentiometer resistance 130, and adjustable along said resistance is a conductor tap131. A second potentiometer resistance 133 is connected across the secondary winding 100 and this resistance is adapted to cooperate with a.

second adjustable-tap 134. Taps 131 and 134 are connected through resistances 136 and 137 in series, resistance 136 bein shunted by a condenser 140. The purpose of these resistances, taps and condenser will be explained later.

The energy for excitin the vplate currents of the vacuum tubes is erived from 'a secondary windin 104 of the supply transformer 90, jwhic 1 for the ordinarycharacteristics of lighting supply by alternating current would be of the step-up form, say volts to. 450 volts. The alternating current energy from the secondary 104 is applied to a rectifier 106 shown as a two-electrode vac-- uum tubewhose filament is heated by alternating current from another secondary winding 108 ofthe transformer 90. The a t ernat-.

ing current from the windin 104- is rectified in amanne'r well understoo in the art and applied to the terminals of the filter formed 1 by two large capacity condensers 110 and 111 7 connected throu h a large inductance coil or choke 112, the ter acting in a well known manner to smooth out-to-a substantial de-' gree half wave impulses resulting from rectification'. 'The smoothed out rectified cur-, rent is applied across the terminals of a, 1

.- higher resistance 115, and I connect the final high power tube 54 across the terminals of this resistance to give the :t-ull voltage of the filter system to the plate circuit of the last tube. This voltage in one of the systems constructed by me is 450 volts. From Fig. 7 it will be seen that the plate of tube 54 is con tive side of the filter.

I connect the plate circuits of tubes 50, 51 and 53 between the negative terminal of the filter system and an intermediate point 118 of the resistance 115, thus impressing on the plates of these tubes a voltage less than the full voltage of the" system. In the system above referred to as constructed by me, I use for the plate circuits of the tubes 50, 51 and 53, a voltage of 12().- The filament return of the plate circuits of tubes 50, 51 and 53 may be traced from the tap 134, resistance 136, conductor 141 to the negative side of the filter. v

The plate circuit of the detector tube 52 is alsoconnected between the negative terminal of the filter and the intermediate point118 of resistance 115, but in order to reduce the voltage applied to the plate of the detector tube to the desired amount for proper-operation of this tube, Iinclude in the lead from the point 118 to the plate of this tube a resistance 120.

I preferably connect a high capacity condenser 150 between the point 118 and the negative end of the filter. This condenser acts as a shunt around the portion of the resistance 115 to the left of the point 118 to permit by-passing of high and low frequency signal currents, and alsoto assist condensers. 111 and 112 in smoothing out the rectified 1 (iii The plate circuit return from the filament Thegrids of all the tubes are connected to current.

the negative terminal of the filter through the conductor 141 inasmuch as the plate circuit returns from the filaments of tubes 50,

51, 52 and 53 pass from potentiometer 133 'through resistance 136, and thence through conductor 141 to the negative side of the filter.

" It will be seen that the grids of these tubes have a negative biasing potential with respect totheir filaments by an amount equal to thepotential drop across the resistance 136 this resistance being selected so as to give the desired grid biasing voltage to these tubes. By employing a drop of the potential created by the'combined plate currents of tubes 50 to 53, resistance-136 may be of relatively small value to give the necessary difi'erence otpotential for furnishing the required grid bias to these tubes. The resistance 136 constitutes a couplirigflement capable of transferring energy from'the plate circuit back to the grid circuit of the tubes as well as from a succeeding tube back to a preceding tnbe-,

and is therefore an element tending to make the-system unstable by regenerative eflecfs' if provision is not made for keeping these ef tects to practical low limits. A step toward this end is accomplished by utilizing the combined plate current to create the desired difa r ference in potentiahthereby making the 're sistance 136 low. Also the'condenser-140- of large capacity shunting the resistance. 136

permits highand low frequency current Variations to avoid the resistance 136 b a low' high reactance or choke coils 161, which serve to exclude the high frequency grid currents irom the resistance'136 and the filter cirbetween one terminalof the primary and the filament of tube '52. A low ,capacity condenser 169 connected between the plate and the filament of tube 52 furnishes a path of lovv impedance for the high frequency components of the plate current of tube '52.

bf power tube 54 passes through the potentiorneter 130, 131 through resistance 137 to the negative conductor 141. As the grid of tube54, is connected to conductor 141, this grid receives a negative biasing potential equal to the potential drop across the 'resist-' ance-"137 ;.resistance 137 bein so selected as to give the partic-ular 'rid iasing voltage required bytube'fi'gt; .vVhile resistance 13 v forms a couplingbetween the grid andplatf- -g circuits oftube 54, these circuits do not carry high frequenc current and are not subject to the disturbing regenerative effectswhichare apt to occur: in the circuits of the preceding tubes, and I find that a shunting condenser for the resistance 137 is-unnecessary. Potentiometer resistances 130 and 133 and the adjustable taps 131-134 furnish a means by which I may eliminate an residual hum in the plate circuit of the fina amp 'fier tube 54 which hum may be caused, foixample, by low frequency variations or ripples in the plate currents due to imperfect filtration ofcurrent supplied by the rectifier 106. By adjustment of the taps 131 and 134 the ids of tube 54 and tubes 50 to 53 respective may be subject to low frequency variations in (potentialrelative' to; the mid points of their respective filament". Such variations impressed on the grid will'be of reateramplitude as the points of contact 0 the ta s with the resistances are farther away from t e midgosite side of the mid-pointof the resistance.

y proper adjustment of these taps these variations of grid potential can be so controlled, both in-amplitude andphase, as to reflect a substantial neutralization of any residual hum which would otherwise occur in the late circuit of the final tube 54.

ile I have shown and described two tubes embod ing my inventions, it will be understood t at these tubes are merely typi-v cal of a number of tubes which have the ad vantages discussed. Inthese tubes 1 have used an electron emitting material consisting of oxide of strontium and barium. Other read. electron'emitting materials are known and y a proper selection of such material it is possible to supply sufiicient electron emission at. a filamenttemperature even lower than the temperature at which I operate the tubes herein disclosed; that is, at a black red heat, and I deem a tube having a filament operated at such low temperature to be within the scope'of the present invention.-'

This application is a continuation in part of my applications Serial No. 117,076, filed June 19, 1926, and Serial No. 50,555, filed August 17, 1925.

I claim:

1. In a vacuum tube, the combination of an electron emissive filament, grid and late; said tube having a bum curve inclu mg a region of hum minimum; said filament having an emissioncurve including an origin of emission saturation; said filament also having such length, resistivity and cross-section that when energized by alternating current said hum minimum occurs at a filament voltage greater than the filament voltage of said origin of emission saturation and at a filament ampera e not greatly differing from said filament vo tage, t e temperature of said filament at said voltage being at least as low as the efi'ective electron emission temperature of strontium oxide.

,2. In a vacuum tube, the combination of an electron emissive filament, grid and plate; said tube having a hum curve including a region of hum minimum; said filament haV-j mg an emlssion curve mcludmg an origin of- .emission saturation at a voltage less than three voltsysaid filament" also having such said voltage being at'least aslow as the efiective electron emission temperature of -strontium oxide.

-3. In a vacuum tube, the combination of an electron emissive filament, grid. and late; said tubehaving a hum curve inclu ing a region of hum minimum; said filament having an emission curve including an origin'of emission saturation at a voltage less than two volts; said filament also having such length, resistivity and cross-section that when energized by alternating current said hum minimum occurs at a filament voltage greater than the filament voltage of said originof emission saturation and at a filament. amperage not greatly differing from said filament voltage, the temperature of said filament at said voltage being at least as low asthe'efiective electron emission temperature of strontium oxide.

4. In a vacuum tube, thecombination of an electron emissive filament, grid and plate; said tube having a hum curve including a region of hum minimum; said filament havng an em sslon curve including an orlgm ofemission saturation at a voltage less than one volt; said filament also having such length,

' resistivity and cross-section that when energized by alternating current said hum minimum occurs at a filament voltage greater than the filament voltage of said origin of emission saturation and at a filament amperage equal to or greater than said filament voltage, the

temperature of said filament at said voltage being at least as low as the efiective emission temperature 'ofstrontium oxide. I

5. In a vacuum tube, the combination of an electron emissive filament, grid and plate; said tube having a hum curve including a region of hum minimum; said filament having an emission curve including an origin of emission saturation said filament also having such length, resistivity and cross section that when energized by alternatlng current said hum minimum occurs at a filament voltage at least as small as the current in amperes oxide.

6. In a vacuumtube, the combination of an electron emissive filament, grid and plate;

said tube having ahum curve-includlnga .regioncf hum minimum; said filament having am emission curve including an origin of emissionsaturation; said filament also having such length, resistivity and cross-section that when energized by alternating current said 7 hum minimum occurs at a filament voltage corresponding to said origin of emission satu-v less in numerical value than the current 1n amperes flowing through said filament which voltage is greater than the filament voltage cross-section that said origin of emission saturationoccurs-at a filament voltage at least as small as the, current in amperes flowing through said filament, at which voltage and amperage the temperature of said filament is at least as low. as said efiective electron emission temperature. .l

8. In a vacuum tube,the combination of an electron emissive filament, grid and plate,

said tube having a hum curve including a region of hum minimum; said region of hum minimum occurring at a filament temperature at least as low as the efic'ective electron emissive temperature of strontium oxide said filament having-an emision curve including an origin of emission" saturation; said filament having such length, resistivity and cross-sect1on that said originof emission saturation occurs at a filament voltage smaller than the current in amperes'flowing through said filament, at which voltage and amperage the temperature of said filament is'at least as low as said effective electron emission tem erature.

9. Ina vacuum tube, the combinatlon of an electron emissive filament, grid and plate, said tube having a hum curve including a region of hum minimum; said region of hum'minimum occurring at a filament temperature at least as lowas the efi'ective electron emissive temperature ofstrontium'oxide; said filament having an emission curve including an origin of emission saturation; said filamenthavin such length, resistivity and cross-section t at said origin of emission. saturation.

occurs at a filament voltage lowerthan two' .volts and filament amperage not greatly ditfering therefrom at whichvoltage and amperage the temperature of said filament is at least as. low as said efiective electron emission temperature.

10. In a vacuum tube, the combination of an electron emissive filament, grid and plate, 881d tube having a hum curve including a region of hum mlnimum; said region ofhum minimum occurring at a filament temperaders it imperfectly visible. 14. In a vacuum tube,-the combination 10f ture at least "as low as the eflective electron emissive temperature of strontium oxide; said filamenthaving an emission curve including an origin of emission saturation; said filament having such length, resistivity and cross-section that said origin of emission saturation occurs at a filament voltage lower than the filament voltage of said region of hum minimum, and at an amperage exceeding the numerical value of said voltage, at which voltage and amperage the temperature of said filament is at least as low as said effective electron emission temperature.-

11. In a vacuum tube, the combination of anelectron emissive filament, grid and plate, said tube having a hum curve including a region of humminimum; said region of hum minimum occurring at a filament tempera- 'ture at least as low as the eifective electron emissive temperature of strontium oxide; said filament having an emission curve including an origin of emission saturation; said filament having such length, resistivity and cross-section that said origin'of emission saturation occurs at a filament voltage less than one volt and a filament amperage greater than one ampere, at which volta e and amper age the temperature of "said temperature.

an electron emissive filament,

ament is at least as low as said effective electron emission v 12. In a vacuum tube, the combination of grid and plate,

said-tube having a hum' curve includin a region of hum m1nimum;-said region 0 hum" I mlmmum occurring at a filament voltage at least 'as' low as the filament voltage corresponding to the effective electron emissive temperature of strontium oxide; said fila:

ment having an emission curve including an origin-of emlsslon saturation; sald filament havin such length, resistivity and cross-section t at-said origin of emission saturation.

occurs at a filament voltage at which said filament is heated to temperature not greater than said efiective electron emissive temperature and at which the current 1n amperes flowing th'rou" h said filament is at least as great as said fi ament voltage.

-13. In a vacuum tube, an electron emissive filament, grid and plate, said tube having a hum curve including a the combination of v region of hunt-minimum; said-region of hum minimum occurring at a filamen t--temperature at least'as low as the efiective electron emissive temperature 'of strontium oxide;

said filament having an emission curve includmgan or1g1n of em1ss1on saturatlon; sald filament having such length,-resistivity and cross-section that said origin of emission saturatlon occurs at a filamentvolta e at which the current in amperes flowing t rough said;

filament is greater than said voltage and at which the temperature of said filament renan electron emission filament, grid and plate; said tube having a hum curve lncludinga relatively broad region of hum minimum; said region of hum minimum occurring at a filamenttemperature at least as low as the eflective electron emissive temperature of strontium oxide; said filament having an emission curve including an origin of emissionsaturation; said filament having such length, re-

sistivity and cross-section that said origin of emission saturation occurs below the fila-I Inent voltage corresponding to said region of hum minimum and the ratio of the difference in potential between any two points of said filament, measured in volts, to the distance apart of said points, measured in inches is less than unity and the operating voltage of said filament does not exceed the current in amperes flowing through said filament.

15. In a vacuum tube, the combination of an electron emissive filament, grid and late; said tube having a hum curve includmg a relatively broad region of hum minimum;' said region of hum minimum occurring at a filamenttemperature at least as low as the effective electron'emissive temperature of strontium oxide; said filament having an emissive curve including an origin of emmission saturation; said filament havin such len th resistivit and cross-section e g a y a,

that saidor1g1n offemissipn saturationoccurs at a voltage below the' filament voltage corresponding to said region of hum minimum and the ratio of the difierence in potential between any two point s of said filament, measured in volts, to the. distance apart of said points, measured-in inches is less than unity and the operating potential across said filament is less than the current 'in amperes flowing through said filament.'

\ In testimony whereof hereunto afiix my signature. BENJAMIN F.MIESSNER. v 

